hi, i have a problem with the boiler cutting off intermittently, when it does it boiler knocks (overheats?) and flame failure LED flashes, when resetting boiler, it restarts, knocks after around 10 secs and faults again. when restarting boiler pump is not running but if using hot water pump can be heard working, if boiler is left a while it will reset and work as normal for around half an hour, hope there is enough information here to help diagnose the fault, thanks Eric